The present invention relates to a process for producing polyether polyols having primary hydroxyl end groups, comprising the steps of reacting a starter compound containing active hydrogen atoms with an epoxide under double metal cyanide catalysis, reacting the resulting product with a cyclic carboxylic anhydride and reacting this resulting product with ethylene oxide in the presence of a catalyst containing at least one nitrogen atom per molecule, excluding non-cyclic, identically substituted tertiary amines. The invention further relates to polyether polyols obtainable by this process, compositions containing said polyols and polyurethane polymers based on said polyols.
Long-chain polyether polyols produced by double metal cyanide catalysis (DMC catalysis) are also known as IMPACT polyethers. The nature of the system is such that they contain predominantly secondary hydroxyl end groups. The use of ethylene/propylene oxide mixes (EO/PO) is possible only up to a certain proportion of EO; for that reason it is not possible to obtain long-chain polyether polyols containing predominantly primary hydroxyl end groups by the impact method. Instead such polyethers are obtained either by catalysing exclusively with conventional base catalysis (for example KOH) or in a two-stage procedure by polymerising an EO end block onto an IMPACT PO polyether obtained by DMC catalysis, optionally a PO/EO mixed polyether or a polyether having PO/EO mixed end blocks, under KOH catalysis.
The KOH method generally has the disadvantage that this catalyst has to be separated off by laborious means, for example by neutralisation and filtration. Furthermore, in the case of long-chain polyethers in particular, undesired olefinic end groups are formed as secondary products. Such olefinic end groups or allyl ether end groups reduce the functionality of these polyethers and make them more difficult to use in certain applications. They also lead to polyurethane (PUR) products, which are of a poorer quality.
U.S. Pat. No. 4,487,853 discloses a process for producing a polyether ester polyol with a high content of primary hydroxyl groups. In this process a) the reaction product of a condensate of a polyol with an alkylene oxide is reacted with a cyclic carboxylic acid and b) ethylene oxide at a temperature of 50° C. to 125° C. The condensate is obtained from a polyol having 2 to 8 hydroxyl groups and an equivalent weight of 30 to 45 and an alkylene oxide having 2 to 4 carbon atoms and mixtures thereof. The condensate has an equivalent weight of 500 to 10,000. Following reaction with the cyclic carboxylic anhydride a semiester is obtained. The reaction of a) with ethylene oxide takes place in the presence of an effective amount of an amine, oxide or divalent metal catalyst. The ratio of equivalents of the anhydride to equivalents of the condensate is in the range from approximately 1:1 to approximately 1:2 and the molar ratio of ethylene oxide to anhydride is in the range from approximately 2:1 to approximately 1.5:1. A polyurethane from the reaction of an organic polyisocyanate with such polyols is also disclosed.
However, U.S. Pat. No. 4,487,853 does not describe how polyether polyols produced under DMC catalysis can be converted into polyols having primary hydroxyl end groups with as little processing effort as possible. There is consequently still a need for alternative production processes for polyether polyols having primary hydroxyl end groups and in particular for such processes which convert polyethers produced with DMC catalysis.